Roman Heavy Cavalry Fighting Techniques

[JeffF]

In reference to the Roman cataphractii/clibinarii of the mid-4th century, reconstructions and illustrations show that these heavy cavalrymen wielded their contos/lance with two hands. I assume this means that the horsemen had to control their mounts using knees and feet only since the use of their weapon required both hands, is this correct? In general how was the lance used? Was the lance held with both hands with the weapon entirely on one side of the horse or was it used across the body with the point of the weapon on one side of the horse's neck and the rear of the lance on the opposite side? These heavy cavalrymen also lacked shields. How did this effect their ability to melee in close combat? They had long swords as a secondary armament but were they at a disadvantage when fighting lighter cavalry when those adversaries had shields?